JPH026598A - Method of decreasing nox content in gasified coal fuel - Google Patents

Abstract

PURPOSE:To continuously eliminate NH3 contained as an impurity in a dry process, by supplying oxygen to a gasified coal fuel at temp. above 700 deg.C. CONSTITUTION:The NOx content of a gasified coal fuel (NH3 concn.: several hundreds to several thousands of ppm) is decreased by mixing the fuel homogeneously with oxygen, oxygen-contg. gases (e.g., or air), or compounds with generate oxygen on evaporation (e.g., H2O2), and treating at temp. above 700 deg.C. When nitrogen oxides (e.g., NO, N2O or NO2) are injected simultaneously with oxygen, they reduce the lower limit of decomposition temp. of NH3 and therefore the treating temp. may be above 600 deg.C. The amt. of injected gas is such that the concn. ratio O2/NH3=1-3, or NO/NH3=0.5-1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for reducing NOx in coal gasified fuel. More specifically, the present invention relates to a dry continuous method for removing ammonia contained in coal gasified fuel as an impurity.

(Conventional technology) In recent years, coal gasification combined cycle power generation has been attracting attention domestically and internationally as a new coal utilization technology that is highly efficient and environmentally friendly.Coal gasification combined cycle power generation is a process in which coal is gasified in a gasifier. ,
This is sulfurized and dedusted using a gas purification device, and then combusted in a gas turbine combustor to generate electricity in the gas turbine. At the same time, the exhaust heat is used to generate steam and the steam turbine also generates electricity.

Incidentally, combustion in such gas turbines and the like involves the production of nitrogen oxides (NOx), which are environmental pollutants that cause photochemical smog.
The amount and concentration that can be released into the environment is strictly regulated.

Therefore, conventional NOx prevention measures generally include the adoption of combustion technology to suppress the generation of NOx, and the adoption of denitrification technology to remove NOx from combustion exhaust gas.

However, the fuel itself has never been considered a problem, and the fuel itself has never been contaminated with ammonia, which causes NOx, to the extent that it becomes a problem.

However, when coal is gasified in a gasifier, a portion of the nitrogen in the coal is converted to ammonia (NH3), so NH3 is contained as an impurity in the coal gasified fuel. Since NHa is easily absorbed by water, NH3 is easily removed when gas purification is performed using a wet method such as a scrubber.

However, in that case, the temperature of the coal gasification fuel decreases, resulting in a decrease in thermal efficiency in the coal gasification combined cycle power generation system. For this reason, there is a demand for a method in which gas purification in a coal gasification combined cycle power generation system is performed in a dry state. However, in that case, the NH9 generated in the coal gasifier will be supplied to the gas turbine combustor at almost the same concentration. The NH3 contained in this fuel easily becomes nitrogen oxides (NOx) during the combustion process.
Convert to

The ammonia concentration generated in a coal gasifier varies depending on the coal type and gasification conditions, but ranges from several hundred pp11 to several thousand pp1.
+i, and the proportion of NOx caused by NH3 in the NOx generated in the gas turbine combustor is high. Therefore, coal gasification combined cycle power generation is used to reduce nitrogen oxides caused by NH9 in coal gasified fuel. There is a need for technology to reduce NOx in system systems.

(Problems to be Solved by the Invention) However, coal gasified fuel has an extremely low calorie (less than 2000 kCa I) and is a difficult to burn gas compared to normal gaseous fuel, and its combustion in a gas turbine combustor has a low flame propagation speed. Because the fuel flows at a faster speed, it becomes increasingly difficult to ignite, resulting in combustion conditions that lack flame stability. Because of this, it is very difficult to establish a combustion technology to reduce nitrogen oxides caused by NHa in the fuel in gas turbine combustors, and research and development is currently underway, but it has not yet been realized. No, NOx in combustion exhaust gas
Catalytic exhaust gas denitrification equipment using ammonia injection is a commonly used method for removing nitrogen oxides, and can be said to be an established technology, but it uses an expensive catalyst and requires replacing the catalyst every 30,000 hours. , installing it in a coal gasification combined cycle power generation system imposes a large burden both in terms of system operation and economically.

Therefore, an object of the present invention is to improve the fuel itself, that is, to provide a method for reducing NOx in coal gasified fuel. Specifically, the purpose of the present invention is to provide a method for continuously removing ammonia from coal gasified fuel in a dry manner.

(Means for Solving the Problems) In order to achieve the above object, the NOx reduction treatment of coal gasified fuel of the present invention involves adding oxygen or oxygen-containing gas or The aim is to mix the compounds that evaporate to produce oxygen as uniformly as possible.

In addition, the NOx reduction treatment of coal gasified fuel of the present invention includes adding nitrogen oxides to the coal gasified fuel containing ammonia together with oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen in a temperature range of 600°C or higher. I am trying to inject it.

In the present invention, the gas containing oxygen is generally air, but is not limited to this, and any gas containing oxygen can be used as long as it does not adversely affect fuel components or combustion. be. Compounds that evaporate to produce oxygen include hydrogen peroxide and the like. In this specification, unless otherwise specified, when expressed as oxygen, it includes oxygen obtained from a gas containing oxygen or a compound that evaporates to produce oxygen gas.

Also, as nitrogen oxides, No, N20. NO2 etc. are suitable. This nitrogen oxide injection lowers the lower limit temperature for ammonia decomposition.

The amount of these injected gases is preferably in the range of 1 to 3 with a ratio of oxygen concentration to ammonia of 02/NH3, and a ratio of nitrogen oxide concentration to ammonia of No/NH3.
3 is preferably in the range of 0.5 to 1, 02/
This is because when the NHa ratio is larger than 1, it is effective in decomposing ammonia, but when it exceeds 3, the amount of generated NO increases to a non-negligible extent, and it is no longer effective in reducing NOx as a whole. Moreover, if it is less than 1, much ammonia will remain without being decomposed.

In addition, if NOx is injected at the same time as oxygen is injected at the above concentration ratio, it has the effect of lowering the lower limit temperature for decomposing NH8, but if the NOx / NHB ratio is less than 0.5, the effect is small, and 1. If it exceeds this, the amount of remaining No. will become a non-negligible amount.

Further, in the present invention, oxygen and nitrogen oxides are preferably partially extracted from the coal gasification combined cycle power generation system between the coal gasifier and the gas cooler of the coal gasification combined cycle power generation system or within the gas cooler. The method is characterized in that the mixed gas diluted with the desulfurized and dedusted coal gasified fuel is most preferably diluted with the extracted coal gasified fuel, and then injected into the coal gasified fuel in a cooled state.

(Operation) Therefore, NH3 in the coal gasified fuel reacts with oxygen and nitrogen oxides and is decomposed into nitrogen (N2) and water (H20).

That is, NH3 in the fuel becomes HCN, CN, and Nll i (NH2) at high temperatures where 02 is present.

N
It produces O or is reduced to N2.

The present invention utilizes the decomposition of NH3 by 02 and the reaction of NO with NH8 accompanying the reaction process to reduce the amount of N in coal gasified fuel.
Attempt to decompose H3. This reaction takes place in the gas phase and does not require a catalyst. Also, since the reaction between NH3 and No takes place only in the coexistence of 02, oxygen is mixed with nitrogen oxides and added to the coal gasified fuel. If injected, NH
a is decomposed by 02 and nitrogen oxides. Also,
The oxygen and nitrogen oxides injected are the N in the coal gasified fuel.
Since the amount is so small as to be several times the maximum concentration of 1-I3, the influence on other compositional changes of the coal gasified fuel is so small that it does not pose a problem.

(Example) Hereinafter, the present invention will be explained in detail based on examples.

First, Fig. 11 shows an outline of a coal gasification combined cycle power generation system that implements the present invention. In the figure, 11 is a coal gasification furnace, and 12 is a coal gasification fuel that cools the coal gasification fuel to a temperature that allows desulfurization and dust removal processing. Gas cooler heat exchanger, like heat exchanger
13 is a cyclone dust collector that collects char (tin) contained in coal gasified fuel, and 14 is a cyclone dust collector that collects H contained in coal gasified fuel.
A cleanup (desulfurization/rm) device removes char and the like that could not be collected by the 2S and the cyclone 13, 15 is a gas turbine, and 16 is a steam turbine.

In this system, a part of the coal gasified fuel purified through the clean-up device 13 is extracted, and the coal gasified fuel is extracted from the clean-up device 13.
After being cooled to near room temperature in 7, cyclone 13
It is used as a carrier gas to return the char collected in the gasifier to the gasifier. At the same time, a part of the extracted coal gasified fuel is used as a gas for diluting oxygen or nitrogen oxides to be injected into the coal gasified fuel just generated in the gasifier 11. After the extracted coal gasified fuel and air are mixed and diffused, the air is preferably further cooled to a low temperature in a cooler 18 and then injected into the fuel flow upstream of the gas cooler 12 or within the gas cooler 12. In this example, air is used as the injected oxygen. The mixed gas of the extracted coal gasified fuel and air is injected into the coal gasified fuel and diffuses at the same time, resulting in a uniform mixed state. Immediately after injection, the high concentration region does not react because the temperature is low, forming a reaction freezing region. As the diffusion progresses, the mixed gas is heated and reaches the reaction temperature. Therefore, the reaction starts when the coal gasified fuel and oxygen are mixed as uniformly as possible.

Note that when a liquid such as a hydrogen peroxide solution is used as the oxygen to be injected, the reaction temperature will not be reached unless lick diffusion, which is cooled by the heat of vaporization, progresses to a certain extent.

Moreover, since it is sprayed in the form of droplets, it has a strong penetrating force and good dispersion. In this case, extracted coal gasified fuel as diluent gas is not required.

Next, FIG. 10 shows the low NOx of the coal gasification fuel of the present invention.
An example of a device for carrying out the oxidation process is shown in the isolation tank, where 2 is a storage tank for storing 02, a gas containing 02, or a compound that evaporates to produce 02, 2 is No., N20. NO
2 is a storage tank for storing nitrogen oxides or compounds that evaporate to produce nitrogen oxides; 3 is a valve that controls the flow rate of oxygen and nitrogen oxides according to a control signal from the NH3 concentration monitoring device 6; and 4 is a gas turbine 15. J?
? A mixer 5 mixes oxygen and/or nitrogen oxide supplied from the tank 1 or 2, and a mixer 5 mixes oxygen and/or nitrogen in response to a signal from a temperature monitoring device 9 that measures and monitors the temperature of the coal gasified fuel. A valve that opens and closes a supply flow path for a mixed gas of oxides and oil gasification fuel 1; 6 is an injection device such as a nozzle that uniformly disperses and supplies the mixed gas into coal gasified fuel; 7 8 is a device that monitors the NH3 concentration in the coal gasification fuel and outputs an instruction signal for the 02 concentration and nitrogen oxide concentration to be injected from the measured value of NH concentration to the control valve 3; 8 is the coal gasification fuel in the flow path; gas sampling pipe for extracting fuel;
9 is a gas temperature measuring device such as a thermocouple; 10 is a temperature monitoring device and a device that determines the optimum injection position from the measurement results of the gas temperature at each position and outputs an opening/closing signal for the valve 5. Since the coal gasified fuel leaving the gasifier usually has a temperature of 1000° C. or higher, ammonia can be decomposed by simply injecting oxygen or the like into it.

(1) Decomposition of NH3 by oxygen (02) Figure 1 shows the concentration of 02 injected and the reaction time when the NHBfi degree in the coal gasified fuel is 1000ρp+iv and the gas temperature is 1000°C. From the 0 diagram showing the relationship between the NHg concentration after l5eC, if the 02 concentration is 150011111 or more, the NHg concentration in the coal gasified fuel will be from 1000 ppl to 1 ppm.
It can be understood that it is broken down into the following. If the 02 concentration to be injected is less than 15001)l)II, it is NH.

The decomposition rate deteriorates, especially rapidly below 1oooppn, for example, for the 02 concentration of 5001)l) II, the NHg concentration is decomposed only to 600ppn+.
At this time, the concentration ratio of 02 to NH3 is 1.5.

In Figure 2, the reaction temperature is 1000℃ and the NH3 concentration is 1100℃.
This figure shows the relationship between reaction time and NHg concentration when 1500 ppl of 02 is injected into 0 ppl of coal gasified fuel. As is clear from the national isolation, NH3 is decomposed in about 0.01 seconds.

In addition, Figure 3 shows that the NH3 concentration in coal gasified fuel is 100%.
0111) In-V G::Item gas temperature is 1ooo
3 is a graph showing the relationship between the decomposition of ammonia by oxygen and the concentration of produced nitrogen oxides in the reaction after 0.1 seconds at .degree. According to this, the molar ratio of 02/NH3 is l
If it is less than 4.5, the ammonia decomposition rate will drop sharply below 90%, and if it is more than 4.5, the concentration of nitrogen oxides produced will exceed 150 pl (11), which can be said to be a tentative guideline for tolerance.
However, in actual reactions, N1(3 and 02) in the coal gasified fuel are not completely and uniformly mixed at a predetermined molar ratio, so locally excess oxygen is generated and No is produced. Therefore, it is preferable to keep it within the range of 1 to 3.

In addition, Figure 4 shows that 02 has a molar ratio of 1.5 times that of NH3.
It is a graph showing the relationship between the reaction temperature and the ammonia decomposition rate after 0.1 seconds when injecting the ammonia.

As is clear from the country's national isolation, the ammonia decomposition rate begins to decline when the temperature falls below 700°C, and the decomposition rate rapidly worsens when the temperature falls below approximately 670°C.

From the above results, it is clear that NH3 in coal gasified fuel is decomposed by injection of 02 at a certain temperature.
When 4 degrees is 1000 ppl, if the 02 concentration to be injected is 1500 ppl or more, the NHs concentration is theoretically 1.
decreases below pHl. When 1500 ppl or more of 02 is injected, the formation of NO due to the reaction between NH3 and 02 is observed. However, if only a small amount of No is generated, the advantage of decomposing NHa is much greater.

(2) Decomposition of NI (decomposition of 3) by nitrogen oxides and 02 Even if only nitrogen oxides are injected into the coal gasified fuel, Nta in the gasified fuel is not decomposed, and NO is only decomposed in the coexistence of 02. For example, Figure 5 shows N in coal gasified fuel.
When 11000pp of H3 is included, the reaction temperature is 100pp.
This graph shows the changes in the concentration of various chemical species over the course of reaction time when 1000 ppn of No as a nitrogen oxide was injected at 0°C. 4 Reaction times were 1. Even after Qsec, N Ha remains at the initial concentration of 1000 ppn.

However, together with No. 10001) I) l 02
When injected, NH3 is rapidly decomposed. Figure 6 shows the respective concentrations of NH9, No, and 02 at the reaction temperature after a reaction time of 0.1 sec when 1000 pu of each of NO and 02 were injected when the NT(a concentration in coal gasified fuel was 1000 ppIl). It is clear from the figure that most of NH3 is decomposed if the reaction temperature is 770°C or higher.

For example, when the reaction temperature is 770°C, the NH3 concentration is approximately 0.
．． It is reduced to O2ppm, and decomposed to about 0.2ppn even at a reaction temperature of 1200°C.

However, in this case, the No concentration increases as the reaction temperature increases, and when the reaction temperature is 1000° C. or higher, the No concentration in the coal gasified fuel becomes 100 pp11 or higher.

Also, what should be noted in Figure 6 is that even if 02 and No are injected together into coal gasified fuel containing NH3, the decomposition reaction of NHa will progress slowly below a certain temperature. . Under the conditions shown in FIG. 6, the most suitable temperature for decomposition is judged to be 770°C.

Figure 7 shows the same concentration of 02 as when 1500 ppl of 02 alone was injected into coal gasified fuel containing 1000 ppn of NH3.
The reaction time when 500 ppi of NO was injected together with 0.
The concentrations of NHs, No., and 02 after 1 sac are shown relative to the reaction temperature. In Figure 7, N 14
The reaction temperature at which the decomposition of a is maximized is 840°C when only 02 is injected, but it drops to 750°C when 500 ppl of No is injected. That is, the effect of injecting No together with O2 is to reduce the reaction temperature range in which the decomposition of NH3 becomes effective. In addition, the reaction temperature is 700℃
If 500 ppm No is added at the same time, NHa? The degree of a is 2 ppn (NH3 shown by the dotted line in the case of no addition), the decomposition rate of NH3 is 99.8%, and even if the optimum reaction temperature is 850°C, the decomposition effect of NH is 700°C. But it's enough. However, 700℃
If the temperature is lowered even slightly in the vicinity of the temperature range, the decomposition of NH3 will deteriorate, so it is practically preferable that the reaction temperature range is 700°C or higher.

Figure 8 shows the relationship between the No concentration injected at the same time and the NH3 concentration and No concentration after a reaction time of 0.1 sec when 02 is injected at 1000 ppH into coal gasified fuel containing NH3 of 1ooOpp+i. The reaction temperature is 1
000℃. If the Nofi degree is 700 ppi or more, NH3 will be decomposed to 1 ppIlpHl or less. However, as the N04 degree to be injected increases, the No concentration remaining in the coal gasified fuel also increases rapidly.

When 2000 ppIl of NO is injected, the No concentration in the coal gasified fuel becomes approximately 100011111 in FIG. 6.

Further, FIG. 9 is a graph showing the relationship between the ammonia decomposition promoting effect due to the addition of nitrogen oxides and the No concentration. As is clear from the national isolation, N O/N H.

It can be seen that when the molar ratio is less than 0.5, the ammonia decomposition rate deteriorates rapidly, and when it exceeds 1.0, the NO production concentration exceeds the allowable concentration.

In this way, by appropriately selecting the 02 concentration and No concentration to be injected and injecting in the optimal temperature range, ammonia can be decomposed within a range where the generated NO and other remaining components do not have a large effect. is important.

For example, the optimal temperature range for the decomposition of NH3 is 02m degrees, which is injected with respect to the NH3 concentration contained in the coal gasified fuel.
o concentration. When the reaction temperature is determined, the 02 concentration and No concentration to be injected to the NH3 concentration in the coal gasified fuel are determined from the NH3 decomposition rate and the No concentration remaining in the gasified fuel.

In the reaction calculation to confirm the ammonia decomposition effect of the present invention, it is assumed that the injected 02 and nitrogen oxides are uniformly mixed in the coal gasified fuel, and the reaction temperature is set at the set initial temperature. It was set as constant.

(Effects of the Invention) As is clear from the above explanation, the present invention involves injecting oxygen, an oxygen-containing gas, or a compound that evaporates to produce oxygen into coal gasified fuel in a temperature range of 700°C or higher. Therefore, NHa in coal gasification fuel
is the No. associated with the reaction process of decomposition of 02 and NH3 by 02.
It is decomposed into nitrogen (N2) and water (H2O) and removed.

Furthermore, by simultaneously injecting nitrogen oxides with O2, the decomposition reaction temperature of NH3 is lowered, thereby promoting the decomposition of NHa more effectively.

Therefore, according to the present invention, NH in coal gasified fuel
3 can be removed dryly, without causing a decrease in the thermal efficiency of the entire system, and because NOx caused by NH3 generated in the gas turbine combustor is eliminated, NOx
This makes it possible to significantly reduce the amount of In addition,
This eliminates the need for a catalytic exhaust gas denitrification device, reducing equipment costs and making the system easier to operate.

[Brief explanation of the drawing]

Figure 1 shows the MHI concentration versus the added 02 concentration, Nof
A graph showing the relationship between i degree and 02, Figure 2 is a graph showing the change in concentration of each chemical species with respect to reaction time, Figure 3 is a graph showing the relationship between 02 and the decomposition of NHa and the generated N0vA degree.
Figure 4 is a graph showing the relationship between reaction temperature and NH3 decomposition rate, Figure 5 is a graph showing the behavior of NH3 when only NO is added, and Figure 6 is a graph showing the state of NH3 decomposition due to the addition of 02 and NO. Figure 7 is a graph showing the relationship between the reaction temperature and the behavior of NH3 and NO, Figure 8 is a graph showing the influence of No addition on the decomposition of NH3, and Figure 9 is a graph showing the effect of No addition on promoting NHa decomposition. A graph showing the relationship with the No concentration, FIG. 10 is a schematic explanatory diagram showing an embodiment of the apparatus for carrying out the NOx reduction treatment of coal gasified fuel of the present invention, and FIG. 11 is a graph showing the relationship between the NOx concentration and the coal gas 1 is a block diagram showing an overview of a combined cycle power generation system. 11... Gasifier, 12... Gas cooler, 14...
-Cleanup device, 18...Cooler.

Claims (8)

[Claims] (1) 700℃ in coal gasified fuel containing ammonia
A coal gasified fuel NOx reduction treatment method characterized by injecting oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen gas in the above temperature range. (2) The amount of oxygen injected is a concentration ratio of O_ to ammonia.
Claim 1 characterized in that 2/NH_3 is 1 to 3.
The coal gasification fuel NOx reduction treatment method described. (3) A coal gasified fuel containing ammonia, which is characterized by injecting nitrogen oxides together with oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen gas in a temperature range of 600°C or higher. Low NOx treatment method. (4) The amount of oxygen injected is a concentration ratio of O_ to that of ammonia.
2/NH_3 is 1 to 3, and the injection amount of nitrogen oxide is 0.5 to 1 with a concentration ratio of NO/NH_3 to ammonia.
4. The coal gasification fuel NOx reduction treatment method according to claim 3, wherein the NOx reduction treatment method is within the range of . (5) The oxygen and nitrogen oxides are injected between the coal gasifier and the gas cooler of the combined coal gasification combined cycle power generation system or within the gas cooler. Coal gasification fuel NOx reduction treatment method. (6) The coal gasified fuel according to claim 5, wherein the oxygen and nitrogen oxides are diluted with desulfurized and dedusted coal gasified fuel extracted from a coal gasification combined cycle power generation system, and then injected. Low NOx treatment method. (7) The oxygen and nitrogen oxides are diluted with desulfurized and dedusted coal gasified fuel partially extracted from the coal gasification combined cycle power generation system, and are cooled before being injected. The coal gasification fuel NOx reduction treatment method described. (8) The coal gasification fuel NOx reduction treatment method according to any one of claims 1 to 5, wherein the compound that evaporates to produce oxygen gas is a hydrogen peroxide solution.